Pressure-sensitive adhesives (PSAs) are adhesives which permit a durable join to the substrate even under relatively weak applied pressure and which after use can be detached from the substrate again substantially without residue. At room temperature, PSAs have a permanently pressure-sensitively adhesive effect, hence having a sufficiently low viscosity and a high initial tack, so that they wet the surface of the particular bonding base even under low applied pressure. The bondability of the adhesives derives from their adhesive properties, and the redetachability from their cohesive properties.
Included in particular under this heading are compounds which possess pressure-sensitively adhesive properties in accordance with the “Handbook of Pressure Sensitive Adhesive Technology” by Donatas Satas (Satas & Associates, Warwick 1999), especially those which meet the Dahlquist criterion.
Elastically or plastically highly extensible pressure-sensitive adhesive strips which can be detached again without residue or destruction by extensive stretching in the bond plane are known from, for example, U.S. Pat. No. 4,024,312 A, DE 33 31 016 C2, WO 92/01132 A1, WO 92/11333 A1, DE 42 22 849 A1, WO 95/06691 A1, DE 195 31 696 A1, DE 196 26 870 A1, DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1, DE 197 08 364 A1, DE 197 20 145 A1, DE 198 20 854 A1 and DE 100 03 318 A1, and are also referred to below as strippable pressure-sensitive adhesive strips.
Strippable self-adhesive tapes of this kind are used frequently in the form of single- or double-sidedly pressure-sensitively adhesive adhesive-sheet strips, which preferably have a nonpressure-sensitively adhesive grip region, from which the detachment operation is initiated.
Fields of use of aforesaid strippable pressure-sensitive adhesive strips include in particular the residueless and nondestructively redetachable fixing of light to moderately heavy articles in the home, workplace, and office. In these applications they replace conventional fastening means such as, for example, drawing pins, roundhead needles, thumb tacks, nails, screws, conventional self-adhesive tapes, and liquid adhesives. Key to the successful use of the pressure-sensitive adhesive strips is not only the possibility of residueless and nondestructive redetachment of bonded articles, but also their quick and easy bonding and also their secure hold for the envisaged period of bonding. It should be borne in mind in particular here that the adhesive strips must function on a large number of substrates, in order to be able to serve as a universal fixing in the home, workplace, and office.
Pressure-sensitive adhesive strips of these kinds are available commercially, in the form of the tesa Powerstrips® and 3M Command Adhesives.
Very high holding performance has been realizable to date, commercially, only with styrene block copolymer-based PSAs. These styrene block copolymers always include unsaturated polydiene blocks. Polydienes are intrinsically susceptible to thermooxidative aging and may be damaged by radiation and ozone.
A further key aspect of such strips, especially when they are to be used on transparent surfaces such as windows, is their transparency.
tesa markets strippable transparent products with moderate holding performance as tesa Powerstrips® Deco. 3M offers transparent adhesive strips featuring a holding performance of up to 900 g.
Approaches to creating transparent strippable adhesive products include the utilization of styrene block copolymers which comprise hydrogenated polydiene blocks (DE 10 2007 021 504 A1 and U.S. Pat. No. 7,309,524 B). Although high transparency and improved aging stability are possible with the solution outlined, the requisitely high bonding performances, and especially the tear resistance, are not achievable via these formulation approaches.
EP 1 418 212 A1 describes transparent adhesive strips, redetachable without residue or destruction, which are of triple-ply design. In this arrangement, the middle layer contributes the major part of the mechanical properties to the product properties, but is unstable toward UV light and ozone on account of its formulation. The outer layers take on a filter function for ozone and UV light. A disadvantage of this approach is its multilayerness, which necessitates a multistage production process. Furthermore, the achievable holding performances are limited due to the adhesive formulation forming the outer layers.
Also known are polyacrylate-based systems (WO 2010/077541 A1; WO 2010/078346 A1; WO 2010/077435 A1; U.S. Pat. No. 6,723,407 B1), and there are also descriptions of polysiloxane-based adhesive strips, including in U.S. Pat. No. 6,569,521 B1 and WO 2009/114683 A1. Advantages are their optical properties and the resistance. The tension/extension properties and the balance between holding performance and bonding performance, however, are not at a level allowing high-performance adhesive strips to be produced. In some such cases, sufficient tear strengths are achievable only through use of a carrier.
Multilayer products or those which include carriers always have the disadvantage either that highly specific machines are required for production, or that a multiplicity of individual process steps have to be carried out. Both of these are detrimental to the production costs.
The object is therefore to provide pressure-sensitive adhesives which exhibit high holding and bonding performance, high transparency, minimal tinting, and sufficient stability with respect to light, heat, and ozone, and sufficient tear strength, and also self-adhesive products comprising such pressure-sensitive adhesives. Corresponding self-adhesive products are preferably of single-layer (carrier-free) design.
This object is achieved by means of a pressure-sensitive adhesive as recorded in the main claims. The dependent claims provide advantageous developments of the pressure-sensitive adhesive, and uses of the pressure-sensitive adhesive in pressure-sensitive adhesive strips.